A diagonal of quadrilateral divides it into unique triangles. Will the sum of parameter of them equal to the parameter of quadrilateral or not?

Answer 1

Draw this figure, and then trace each triangle.

You should notice that you have traced a line segment (twice) that is not any side of the quadrilateral...

So no: the sum of the perimeters of the triangles does not equal the sum of the quadrilateral, it is more.

Answer 2

Simply put, no. Did you draw and label a diagram.

The diagonal counted twice for the perimeter of the two triangles does not belong to the perimeter of the quadrilateral.